At a recent meeting on sustainability, the company unveiled the Wal-Mart Advanced Vehicle Experience, a new concept truck that's 20 percent more aerodynamic than its current fleet. The WAVE features a micro-turbine power-train that can run on diesel, natural gas, biodiesel, and potentially new forms of fuels still in development. The trailer is also made almost exclusively with carbon fiber, which sheds around 4,000 pounds of body weight.

Wal-Mart just began formally testing the WAVE, but there's no guarantee it'll actually make it onto the road.